1. Field of the Invention
The present invention relates to a method for fabricating a liquid crystal display device and, more particularly, to an apparatus for forming an alignment layer of a liquid crystal display device and method for forming an alignment layer using the same.
2. Description of the Related Art
With recent developments of various portable electronic devices, such as mobile phones, personal digital assistants (PDAs), and notebook computers, demand for light weight, thin profile, small flat panel display devices is increasing. Present research includes active development of the flat panel display devices including liquid crystal display (LCD) devices, plasma display panel (PDP) devices, field emission display (FED) devices, and vacuum fluorescent display (VFD) devices. Of these different devices, the LCD devices are actively being developed due to the simple mass-production techniques necessary to produce them, their easy driving systems, and implementation of high picture quality.
FIG. 1 is a cross sectional view of a liquid crystal display device according to the related art. In FIG. 1, a liquid crystal display device 1 includes a lower substrate 5, an upper substrate 3, and a liquid crystal layer 7 formed between the lower and upper substrates 5 and 3. The lower substrate 5 is a driving unit array substrate and includes a plurality of pixels (not shown), wherein each pixel includes a driving unit, such as a thin film transistor. The upper substrate 3 is a color filter substrate and includes a color filter layer for implementing a color.
A pixel electrode and a common electrode are respectively formed on the lower substrate 5 and the upper substrate 3. In addition, an alignment layer for aligning liquid crystal molecules of the liquid crystal layer 7 is formed on the pixel electrode and on the common electrode. The lower substrate 5 and the upper substrate 3 are attached by a sealing material 9, and the liquid crystal layer 7 is formed therebetween. The liquid crystal molecules of the liquid crystal layer 7 are driven by a driving unit formed at the lower substrate 5, wherein a quantity of light transmitted through the liquid crystal layer 7 is controlled to display an image.
FIG. 2 is a flow chart of a method for fabricating a liquid crystal display device according to the related art. In FIG. 2, the fabrication process of the liquid crystal display device is roughly divided into a driving unit array substrate process for forming a driving unit at the lower substrate 5, a color filter substrate process for forming the color filter at the upper substrate 3, and a cell process.
In FIG. 2, a step S101 includes forming a plurality of gate lines and a plurality of data lines on the lower substrate 5 using the driving device array process for defining a plurality of pixel areas. The step 101 includes formation of thin film transistors, and driving devices that are connected to the gate lines and the data lines at the pixel areas. In addition, the pixel electrode, which is connected to the thin film transistor through the driving device array process, is formed. The pixel electrode drives a liquid crystal layer when a signal is transmitted through the thin film transistor.
A step S104 includes formation of a color filter layer of R, G, and B colors, and formation of a common electrode on the upper substrate using the color filter process.
Steps S102 and S105 both include formation of alignment layers on the upper and lower substrates, wherein the alignment layers are rubbed to provide the liquid crystal molecules of the liquid crystal layer formed between the upper and lower substrates with an initial alignment and surface fixing force (i.e., pre-tilt angle and orientation direction).
A step S103 includes scattering a plurality of spacers onto the lower substrate for maintaining a uniform cell gap between the upper and lower substrates.
A step S106 includes formation of a sealing material along an outer portion of the upper substrate.
A step S107 includes attaching the upper and lower substrates together by compressing the upper and lower substrates together.
A step S108 includes dividing the attached upper and lower substrates into a plurality of individual liquid crystal panels.
A step S109 includes injection of the liquid crystal material into the liquid crystal panels through a liquid crystal injection hole, wherein the liquid crystal injection hole is sealed to form the liquid crystal layer.
A step S110 includes testing the injected liquid crystal panel.
Operation of the LCD device makes use of an electro-optical effect of the liquid crystal material, wherein anisotropy of the liquid crystal material aligns liquid crystal molecules along a specific direction. Accordingly, since control of the liquid crystal molecules significantly affects image stabilization of the LCD device, formation of the alignment layer is critical for fabricating an LCD device that produces quality images.
FIG. 3 is a schematic cross sectional view of a method for forming an alignment layer using a roller coating method according to the related art. In FIG. 3, an alignment material 21 is uniformly supplied using a dispenser 20 having an injector shape between an anylox roll 22 and a cylindrically-shaped doctor roll 23 as the anylox roll 22 and the doctor roll 23 rotate. Then, the alignment material 21 formed on a surface of the anylox roll 22 is transferred onto a rubber plate 25 when the anylox roll 22 rotates to contact a printing roll 24 upon which the rubber plate 25 is attached. The rubber plate 25 is aligned with a substrate 26 upon which the alignment material 21 will be applied, and a mask pattern is formed on the rubber plate 25 in order to selectively print the alignment layer on the substrate 26.
As a printing table 27, upon which the substrate 26 is loaded, is moved to contact the printing roll 24, the alignment material 21 is transferred onto the rubber plate 25 and is re-transferred onto the substrate 26 to form an alignment layer. Since a thickness of the alignment layer is about 500–1000 Å, thickness differences of 100 Å of the alignment layer may generate a blot on the screen of the LCD device. Accordingly, uniform thickness of the alignment layer is critical to display quality images on the screen of the LCD device.
However, since the dispenser 20 supplies the alignment material 21 onto the anylox roll 22 using a left-to-right motion along an upper part of the anylox roll 22, uniform thickness of the resulting alignment layer may not be achieved. For example, as a size of the substrate 26 increases, it becomes increasingly more difficult to form the alignment layer having a uniform thickness. Moreover, since all of the alignment material 21 transferred onto the rubber plate 25 is not necessarily perfectly re-transferred onto the substrate 26, a significant amount of the alignment material 21 is wasted, as compared to the amount of alignment material 21 that is re-transferred onto the substrate 26. Accordingly, the amount of wasted alignment material 21 unnecessarily increases production costs. In addition, when a model of the LCD device changes according to the size of the substrate, the doctor roll, anylox roll, and printing roll must be replaced. Moreover, since a cleaning process is periodically performed, the process is complicate and productivity deteriorates. Furthermore, as the substrate is enlarged in size, the size of the anylox roll and the printing roll inevitably increases. That is, as the size of substrates increases, the corresponding fabrication equipment also increases, thereby making it difficult to maintain a uniform thickness of the alignment layer.